Conventionally, in an electrophotographic device or an electrostatic recording device, an electric latent image or a magnetic latent image is visualized with a toner. For example, in electrophotography, an electrostatic latent image formed on a photoconductor is developed with a toner to form a toner image. The toner image is typically transferred onto a transfer material (e.g., paper), and then fixed upon application of heat.
In recent years, toners have been demanded to be fixed at lower temperatures. This demand results from energy saving achieved by reducing energy for fixing and also from requirements for increasing process speed and image quality of image forming apparatus. In addition, as a result of diversification of usage purposes of image forming apparatus, requirements for low-temperature fixing have been being increasing.
A toner can be fixed at lower temperatures by decreasing its softening temperature. However, decreasing the softening temperature decreases its glass transition temperature to impair heat resistance storage ability. In addition, hot offset resistance is also impaired due to a drop in the lower-limit fixing temperature (i.e., the lower-limit temperature at which fixing can be performed without causing problems on image quality) and to a drop in the upper-limit fixing temperature (i.e., the upper-limit temperature at which fixing can be performed). Therefore, it is difficult to achieve a toner that is satisfactory in all of low-temperature fixing property, heat resistance storage stability, and hot-offset resistance only by controlling a thermal property of the resin itself. There is a demand for providing a toner that is satisfactory in all of low-temperature fixing property, heat resistance storage stability, and hot-offset resistance and that allows to form a high-quality image for a long period of time.
For the purpose of achieving satisfactory low-temperature fixing property, heat resistance storage stability, and hot-offset resistance, for example, there is disclosed a toner containing a crystalline polyester, a non-crystalline polyester, and an inorganic nucleating agent (e.g., see PTL 1).
There is also disclosed a toner which contains a binder resin and has a molecular weight distribution having at least one peak in a range of 1,000 to 10,000 and a half value width of 15,000 or less, where the molecular weight distribution is obtained by GPC of THF soluble matter of the toner (e.g., see PTL 2).
Furthermore, there is disclosed a toner which contains a crystalline polyester resin and has a molecular weight distribution having a main peak in a range of 1,000 to 10,000 and a half value width of 15,000 or less, where the molecular weight distribution is obtained by GPC of THF soluble matter of the toner (e.g., see PTL 3).
Meanwhile, there is disclosed a toner containing 0.01% by weight to 20% by weight of calcium carbonate (e.g., see PTLs 4 and 5). However, it has not been described that a combination with the above-described specific molecular weight distribution results in satisfactory low-temperature fixing property, heat resistance storage stability, and hot-offset resistance or that the calcium carbonate has an elasticity enhancing effect.
It is practically problematic that a manufacturing cost is increased in our rage for high quality. There is a practical demand for ensuring good quality while keeping the cost low, that is, for providing a toner which is satisfactory in low cost and high quality.
However, the above-disclosed methods cannot achieve a toner which is satisfactory in terms of practical use, that is, in economical and qualitative aspects (i.e., satisfactory in all of low-temperature fixing property, heat resistance storage stability, and hot-offset resistance), so that there is a room for further improvement in the methods.